The present invention relates to a display device for displaying input display data, and a display driving circuit for generating a gray-scale voltage according to display data and applying the gray-scale voltage to display elements of a display panel. In particular, the present invention relates to a display device such as a liquid crystal display, a plasma display, and an EL (Electronic luminescence) display, and its display driving circuit.
As for conventional techniques, a conventional liquid crystal driving circuit is disclosed in JP-A-10-240192. This liquid crystal driving circuit generates a gray-scale voltage group of a plurality of levels by conducting resistor division on reference voltages of a plurality of levels by use of string resistors, selects one voltage from among the generated gray-scale voltage group according to input display data, and outputs the selected gray-scale voltage. The reference voltages of the JP-A-10-240192 are stabilized by buffer circuits using amplifiers.
In JP-A-10-301541, there is disclosed a liquid crystal driving circuit of gray-scale voltage selection type. This liquid crystal driving circuit converts a digital video signal to 16 gray-scale levels by using a decoder, inputs decoded outputs of respective colors to counters via OR gates provided respectively for gray-scale levels, counts the number of times of writing each gray-scale level in one horizontal scanning interval, selects one of current sources according to the number of times by means of a selection switch, and supplies the selected current source to a gray-scale voltage output buffer as its bias current. As a result, only a minimum required driving current according to input display data can be flown on each occasion. Therefore, a higher efficiency and a low power consumption can be realized.
In the aforementioned JP-A-10-240192, a certain constant steady-state current is flown through the buffer circuit and the string resistors so as to be able to conduct driving no matter which gray-scale voltage assumes all selection state. The steady-state current is not required for gray-scale voltages that are not selected. If a constant steady-state current is always flown through every buffer circuit and string resistors, therefore, the efficiency is lowered.
In the aforementioned JP-A-10-301541, display data are input continuously. Therefore, it is necessary to always conduct operation of calculating the number of times of selection of each graduation voltage. As a result, the power consumption of a computation circuit portion is excessively large.
An object of the present invention is to provide such a display device and a display driving circuit thereof that power consumption can be reduced by making the steady-state currents efficient or reducing the operation frequency.
In accordance with the present invention, a display device or a display driving device includes a display memory for storing display data; a histogram memory for storing frequencies of gray-scale voltages every line; and a gray-scale voltage generation circuit for generating a plurality of gray-scale voltages on the basis of reference voltages, a current quantity of a circuit for generating each of the plurality of gray-scale voltages being changed according to a frequency of the gray-scale voltage.
Furthermore, in accordance with the present invention, a display device or a display driving device includes a detection circuit for detecting a current quantity of each of gray-scale voltages to be applied to a display panel, and calculating frequencies of the gray-scale voltages every line; a histogram memory for storing frequencies of gray-scale voltages; and a gray-scale voltage generation circuit for generating a plurality of gray-scale voltages on the basis of reference voltages, a current quantity of a circuit for generating each of the plurality of gray-scale voltages being changed according to a frequency of the gray-scale voltage.
According to the present invention, there is brought about an effect that power consumption can be reduced by making the steady-state currents efficient or reducing the operation frequency.